1. Field of the Invention
The present invention relates to a recording medium for recording content data, a recording method and an apparatus for recording content data, and a reproducing method for reproducing content data, in particular to those that allow a conventional reproducing apparatus to reproduce content data and copyright of content data to be protected.
2. Description of Related Art
A new type optical disc from which a conventional CD-DA (Compact Disc Digital Audio) player and a CD-ROM (Compact Disc Read Only Memory) can reproduce data and that has a compatibility with a computer has been developed. In the new type optical disc, content data is encrypted and recorded so as to protect the copyright thereof. It is considered that key information for encrypted content data will be recorded in a lead-in region.
In other words, when content data is encrypted and recorded, there is a problem about the position of the key information. To safely manage key information, it is preferred to store it at a position the user cannot easily access. Thus, when video data is recorded to for example a DVD (Digital Versatile Disc), key information is recorded in a read-in area and encrypted data is recorded in a program area. Thus, in such a new type optical disc, to prevent the user from easily accessing key information, it is considered that the key information is recorded in the lead-in area.
In the case of the DVD, since it has been developed on condition that content data is encrypted to protect the copyright it. Thus, when key information is recorded in the lead-in area, no considerable problem occurs. However, in the case of such a new type optical disc, if key information were recorded in a lead-in area, the conventional player and drive, which cannot deal with the new type optical disc, could not reproduce content data.
In other words, the conventional CD-DA disc and CD-ROM disc have not been developed on condition that encrypted content data is recorded. Thus, the conventional player and drive do not have a function for decrypting encrypted content data. When encrypted data that is read from the new type optical disc is decrypted by the conventional player and drive, it is considered that a decrypting process for content data is performed by software.
However, while the conventional player and driver are reproducing content data from an optical disc, the lead-in area cannot be accessed by the software. In other words, in the CD-ROM standard, the disc is accessed sector by sector, each of which is composed of 98 frames. While the conventional player and drive are reproducing content data, they access the disc sector by sector. Thus, the conventional player and drive cannot access the lead-in area. Consequently, when key information is recorded in the lead-in areas, since the conventional player and drive, which cannot deal with such the new type optical disc, cannot access the key information, they cannot decrypt content data.
A player and a drive that can deal with the new type optical disc will be released after it is decided that key information is recorded in the lead-in area. The player and drive will be designed so that they access the lead-in area, obtain key information, and decrypt encrypted content data with the obtained key information. Thus, when the player and drive that can deal with the new type optical disc become common, the problem of the conventional player and drive that cannot access key information in the lead-in area and reproduce content data will be solved.
In a transitional period until the player and drive that can deal with the new type optical disc become common, the conventional player and drive, which cannot deal with the new type optical disc, reads encrypted content data from the new type optical disc and decrypts the encrypted content data. In such a transitional period, however, since the key information in the lead-in area cannot be accessed, there will be a problem of which encrypted content data cannot be decrypted.
To solve such a problem, it is considered that key information is recorded in a program area so that the conventional drive and player, which cannot deal with the new type optical disc, can decrypt content data.
However, the secrecy of key information recorded in the program area is lower than that recorded in the lead-in area. Thus, when key information is recorded in the program area, although the conventional drive and player, which cannot deal with the new type optical disc, can decrypt content data, the key information recorded in the program area is illegally taken out. As a result, it is considered that since the content data will be illegally reproduced and copied, the copyright thereof cannot be protected.
Therefore, an object of the present invention is to provide a recording medium, a recording method and apparatus, and a reproducing method that allow a reproducing apparatus that cannot deal with encrypted content data to decrypt encrypted content data and that the copyright thereof to be securely protected.